Energy absorbing steering column

ABSTRACT

A dual stage energy absorbing steering column includes a support jacket unit comprised of three concentrically arranged jacket members, the inner and intermediate ones of which include a deformer ball type of energy absorber responsive to a first level of impact force on the jacket unit to collapse and absorb energy, the outer jacket member including an energy absorbing plastically deformable section generally coextensive the length of the intermediate jacket member and crushable under some other level of impact force to absorb energy, releasable shear pins engaged between such outer and intermediate jacket members and of a strength selected to effect a desired order of occurrence of energy absorption as between the two energy absorbers.

United States Patent 1 Farrell July 31, 1973 ENERGY ABSORBING STEERINGCOLUMN [75] Inventor: Robert C. Farrell, Saginaw,

Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: May 16, 1972 [21] Appl. No.: 253,788

[52] U.S. Cl. 74/492 [51] Int. Cl 862d 1/18 [58] Field of Search 74/492,493

[56] References Cited UNITED STATES PATENTS 3,470,761 10/ 1969 Okamotoet al. 74/492 R'im wm lrM u m Attorney-W. E. Finken and D. L. Ellis 57ABSTRACT A dual stage energy absorbing steering column includes asupport jacket unit comprised of three concentrically arranged jacketmembers, the inner and intermediate ones of which include a deformerball type of energy absorber responsive to a first level of impact forceon the jacket unit to collapse and absorb energy, the outer jacketmember including an energy absorbing plastically deformable sectiongenerally coextensive the length of the intermediate jacket member andcrushable under some other level of impact force to absorb energy,releasable shear pins engaged between such outer and intermediate jacketmembers and of a strength selected to effect a desired order ofoccurrence of energy absorption as between the two energy absorbers.

3 Claims, 4 Drawing Figures ea 50 56 42 as I Is Patented July 31, 1973 2Sheets-Sheet 1 v Patented July 31, 1973 2 Sheets-Sheet 2 M. WM

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ENERGY ABSORBING STEERING COLUMN This invention relates to energyabsorbers and more particularly to impact energy absorbers forautomotive steering columns and the like structured to effect two ormore stages or levels of energy absorption.

In collapsible automotive vehicle steering columns and similarapplications, it has been found desirable to incorporate energyabsorbing structures arranged to provide staged or differing levels ofenergy absorption arising from differing amounts of force sustainable inthe energy absorberduring different portions of the displacementthereof. Such an arrangement is useful, for example, in steering columnswhere a first low level of force is sustained in the absorber over afirst short amount of displacement in which extraneous forces such asfriction and inertia also usually act briefly to resist steering columndisplacement, thereby to hold the total force in such first displacementportion at an acceptable value. Following the disappearance of theextraneous forces, the energy absorber is allowed to sustain a higherforce to gain a maximum amount of energy absorption.

The present invention has as its principal object to provide such astaged energy absorber, particularly for use in automotive collapsiblesteering columns, and which further economizes on the space occupied bythe column and maximizes the amount of displacement available to theenergy absorber within the space occupied.

One feature of the invention is that it provides energy absorbingconstruction for collapsible steering columns or the like includingthree concentrically arranged tubular members, two of which are engagedby deformer ball or like energy absorbing construction to be operativeas a telescopic assembly for a first mode of energy absorption, while anouter third member, coextensive with the next adjacent inner member, issubject to a predetermined force to provide another mode of energyabsorption through crushing or foreshortening plastic deformation of itslength relative to the adjacent inner member. Another feature of theinvention is that a releasable interconnection is provided between themembers designed to release under a force selected to effect the orderof occurrence of the two energy absorbing modes of displacement withinthe energy absorber.

These and other features and advantages of the invention will be readilyapparent from the following specification and from the drawings wherein:

FIG. 1 is a fragmentary partially broken away elevational view of anautomobile having a steering column which includes an energy absorberaccording to this invention;

FIG. 2 is an enlarged sectionalview taken generally along the planeindicated by lines 2--2 of FIG. 1;

FIG. 3 is a view similar to FIG. 2 showing the steering column collapsein one order of energy absorption occurrence; and

FIG. 4 is a view similar to FIG. 3 showing the steering column modifiedto collapse in a reverse order of energy absorption occurrence.

Referring now particularly to FIG. 1 of the drawings, an automotivevehicle body 10 includes a steering column assembly 12 incorporating anenergy absorber construction according to this invention. Such columnassembly is of conventional type including a steering wheel 14 adaptedfor connection to the vehicle steering gear, not shown, by way of asteering shaft indicated at 16 in FIG. 2. Such shaft has connection atits lower end with a coupling 18 associated with an input shaft elementof the steering gear. Intermediate the steering wheel 14 and coupling18, the steering shaft is supported rotatably on the vehicle body 10 bya collapsible energy absorbing support jacket assembly 20.

Such support jacket assembly 20, and the telescopeable steering shafttherewithin, constitute a rigid column for supporting steering wheel 14in the normal position, shown in full lines, except upon the applicationof some predetermined force to the steering wheel from impact by thedrivers torso thereon as will be described. Thus, support jacketassembly 20 typically includes bearings therewithin, not shown,rotatably supporting the steering shaft within the support jacketassembly and the support jacket assembly is in turn mounted on thevehicle body 10, particularly the forward cowl or plenum structurethereof 22 by a steering column support bracket structure 24. Suchbracket structure includes a lower portion 26 fixedly attached by screwsor the like, not shown, at its lower distal end to the lower end of thesupport jacket assembly 20. If desired, such lower bracket portion 26may extend through an opening in the firewall 28 of the vehicle body asshown, to provide for maximum spacing of the support jacket assemblybetween its lower end and a further portion 30 of bracket structure 24adjacent the upper end of the support jacket assembly. Such upperbracket portion 30 may include a pair of laterally spaced verticallydepending guide flanges 32 merging with a generally horizontaltransversely extending pair of ramp portions 34 suitable for bothlateral and vertical constraint to the path of forwardly collapsingmovement with the support jacket assembly of a generally U-shaped columnbracket 36 which may be welded or otherwise fixedly attached inconventional manner on the upper portion of the steering column supportjacket assembly 20 as is known in the art. A brace member 38 dependsfrom plenum structure 22 for connection with the upper distal end ofupper bracket portion 30 for further'rigidity of steering column supportin known manner. The connection between the upper bracket portion 30 andthe column bracket 36 is structured in a manner to have firm support ofthe upper portion of the steering column on plenum structure 22 duringnormal vehicle operating conditions, but releasable under predeterminedforce applied generally along the axis of the steering column andforwardly thereof to permit relative movement in that direction betweenthe support jacket assembly 20 and its column bracket 36 from theposition shown and down the guide flanges 32 and ramp portions 34.Further, such connection will not permit relative column movement in theopposite direction under forces applied to the lower end thereof fromcollisions causing the steering gear box to move rearwardly relative tofirewall 28. Such a bracket interconnection is disclosed for example, inUS. Pat. No. 3,476,345 to Ristau, issued Nov. 4, 1969, and assigned tothe assignee of the present invention.

Referring now particularly to FIG. 2 of the drawings,

the energy absorbing collapsible support jacket assembracket portion 26connected to it, while upper jacket 44 extends upwardly to steeringwheel 14, as best seen in HO. 1. The three jacket members are arranged,in a-manner to be described, to have separate energy absorbingcollapsible functions between two distinct pairs,

therewithin; i.e., a first collapsible energy absorbing mode betweenlower jacket 40 and intermediate jacket 42 and a second collapsibleenergy absorbing mode between intermediate jacket 42 and upper jacket44. In this way the steering column support jacket may be designedconveniently to exhibit staged levels of energy absorption and forwardcollapse under the application of some predetermined impact force onsteering wheel 14 sufficient to release the interconnection betweenupper bracket portion 30 and column bracket 36. Such staged energyabsorption is useful to control the amount of force sustained in thesteering column and on the driver's torso over the entire collapsedistance necessary to dissipate the energy of the impact. It isparticularly useful in providing a first mode of energy absorption at alow level of sustained force during the initial brief time period ofcollapse of the column when such additional extraneous forces asfriction in the brackets and inertia of the upper steering columnportion are resisting forward movement of the latter. To avoid theseforces causing too high total force sustained in the column duringcollapse, the first mode of energy absorption and force sustained in thefirst mode energy absorber is made relatively low. Following this briefinitial period and the disappearance of the extraneous forces, thesecond energy absorbing mode may come into play at a force levelgenerally equal to that total force exhibited in the first initialperiod of collapse. Thus, a square wave characteristic may be embodiedin the steering column including the combined energy absorbing unitwhere a maximum force presented to the drivers torso is kept at agenerally constant level, which of course maximizes the total energydissipated.

The first energy absorbing mode may be accomplished by incorporation ofa deformer ball type energy absorber including lower jacket 40 andintermediate jacket 42. Such an energy absorber is described in detailin U.S. Pat. No. 3,392,599 to White, issued July 16, 1968, and assignedto the assignee of the present invention. Reference should be had tothat patent for a complete understanding of the absorber but generallyit includes axially spaced annular rows or groupings of deformer balls46 and 48 interposed between jackets 42 and 44 with a predeterminedinterference fit. Thus, each of the balls 46 and 48 are predeterminedlylarger than the annular gap between the outer cylindrical surface of thelower jacket 40 and the inner cylindrical surface of the intermediatejacket 42. Further, balls 46 and 48 are predeterminedly harder than thematerial of the walls of either or both of such jackets. When assembledbetween such jackets, as shown in FIG. 2, the balls 46 and 48 aresubject during telescopic displacement between the jackets to roll overthe walls thereof and plow or furrow grooves therein by localizedplastic strain in the walls. All of the balls 46 and 48 accordingly rollgrooves extending approximately half the distance of the relativecollapsing displacement between jackets 40 and 42 and preferably rollsuch grooves at different circumferential points about the walls of thejackets by properly angularly spacing the balls so that no two rollinglongitudinal pathways of any of the balls 46 and 48 will coincide. 62absorbing The second mode of energy absorption may be achieved, asillustrated herein, by constructing upper jacket 44 as an axiallycrushable member subject to controlled plastic deformation andforeshortening under the application of predetermined force axiallytherethrough. The upper jacket 44 may thus include a crushable energyabsorbing portion 52 formed of an axial series of radially expandedcorrugations 54 extending from adjacent a fairly short cylindrical oruncorrugated section at the jacket lower end upwardly toward the upperend of intermediate jacket 42. Such energy absorbing structure isdisclosed in U.S. Pat. No. 3,373,629 to Wight et al., issued Mar. 19,1968 and assigned to the assignee of the present invention. As disclosedin detail therein, energy absorbing portion 52 may be formed from atubular blank in which diamond shaped perforations are provided todefine a lattice of interconnected strips thereby to furtherintentionally weaken the energy absorbing portion 52 so as to be subjectto collapse in controlled manner under some predetermined axial forceafter the annular corrugations 54 are provided therein. The corrugationsdefine localized bending areas adjacent the end points 58 and 60 of eachof the sides of each corrugation formed in energy absorbing portion 52by the perforations therein. Each of the corrugations 54 are subject,upon application of predetermined axial force, to expand furtherradially outwardly and bend the strips 56 in the lattice formationtherewithin by plastic deformation to dissipate the energy of collapse.

The three jacket members 40, 42 and 44 are assembled in a manner toeffect a desired order of energy ab sorption and collapse as between thetwo distinct pairs within such set of jackets. Thus, the lowercylindrical end 62 of upper jacket 44 is fixedly secured to intermediatejacket 42 by reversely bending the lower marginal end of the latter overjacket end 62. Relative movement between the joined portions of thesejackets is thus prevented when downwardly directed axial force isapplied to upper jacket 44. If desired, jacket end 62 may be welded atthis interconnection with intermediate jacket 42.

Adjacent the upper end of intermediate jacket 42, a releasable shear pinconnection is-provided between it and upper jacket 44 above the energyabsorbing portion 52 of the latter. Such shear pin structure is providedby forming an annular depression 64 in the wall of the upper end ofintermediate jacket 42 and a series of perforations 66 in upper jacket44 communicating with depression 64. Thermoplastic or like material maythen be injected through perforations 66 to fill the latter and theannular depression 64 by molding in situ. When cured, the portion of themolded plastic structure within perforations 66 provide shear pinsfrangible under predetermined axial load sustained in jackets 42 and 44to allow forward displacement of the upper jacket 44 relative to theintermediate jacket 42.

As mentioned, this releasable interconnection features a selected orderof occurrence of the energy absorption available in the two distinctenergy absorbing structures provided by deformer balls 46 and 48 on theone hand, and the energy absorbing portion52 on the other. As mentioned,both such energy absorbing structures will remain in their uncollapsedcondition until some predetermined axial force is applied thereto. Thisfact, in conjunction with a selection of the strength of the plasticshear pins, as by choice of material or crosssectional size ofperforations 66, is utilized to cause staged collapsing and energyabsorption between the two energy absorbers independently of oneanother. One order of occurrence of such energy absorption isillustrated in FIG. 3 where the strength of the plastic shear pins isselected to resist axial force applied to steering wheel 14 at alevelhigher than that which can be resisted by deformer balls 46 and 48without rolling. In this case, the interference fit of deformer balls 46and 48, as adequately explained in the above mentioned White patent, isselected such that a first low level of predetermined force will causethese balls and sleeve 50 to displace and plow grooves in the two jacketmembers 40 and 42 and permit telescopic collapse therebetween. Themaximum amount of such collapse is particularly illustrated in FIG. 3where it is seen that the unit comprised of upper jacket 44 andintermediate jacket 42 is telescopically displaced to abut the lowerjacket end 62 and the lower end of jacket 42 against the collarformation on the lower support jacket portion 26. Further suchtelescoping is thus prevented and if further energy is to be absorbed,the force sustained in the steering column immediately rises as a stepfunction to that predetermined force which will collapse energyabsorbing portion 52. The strength of the shear pins is preferably setsignificantly below this last mentioned predetermined force so that loadis immediately applied to energy absorbing portion 52. Upon theattainment of the predetermined force sustainable in such portion, thisportion collapses in controlled manner and allows relative displacementof the upper jacket 44 relative to the two jackets 40 and 42 which arein effect grounded upon the vehicle plenum structure 22 by lower bracketportion 26. This higher level of energy absorption and force sustainmentwill continue until the energy absorbing portion 52 is fully collapsedas described in the Wight et al patent.

An alternative order of occurrence of energy absorption is illustratedin a modification shown in FIG. 4. There, the predetermined collapseresistance of energy absorbing portion 52 and the plastic shear pinshave been designed to be of a strength lower than the effective strengthor resistance to rolling of balls 46 and 48. Accordingly, uponapplication of a predetermined low load, the steering wheel 14 and theshear pins fracture and force application at the level predetermined forcollapse of energy absorbing portion 52 causes suc collapse anddisplacement of upper jacket 44 relative to the stationary unitcomprised of lower jacket 40 and intermediate jacket 42 which isgrounded on the vehicle plenum structure 22. If impact energy remainsfollowing full collapse of energy absorbing portion 52, the loadsustained in the steering column rises immediately to that which willbegin rolling of balls 46 and 48, whereupon a second stage of higherenergy absorption and load sustainment is effected in accordance withsome selected interference fit characteristic of the assembly includingballs 46 and 48. This interference fit is of course greater, withrelation to the strengths of the plastic shear pins and energy absorbingportion 52, than is the case in the embodiment of FIG. 3.

In accordance with another feature of this invention, it is seen thatupperjacket 44 coextends at least the full length, and is preferablylonger than the intermediate jacket 42. The energy absorbing portion 52is, as illustrated here, generally coextensive the length of suchintermediate jacket but may be shorter if desired, particularly in thecase of the FIG. 4 embodiment where this portion provides the initialenergy absorption mode. At any rate, by having the lower end of upperjacket 44 connected to the lower end of jacket 42 in the describedmanner, a maximum amount of total displacement is available to thesupport jacket assembly 20 without unduly extending the uncollapsedlength thereof as indicated in FIG. 1. A suitable amount of energyabsorption, at suitable load levels, is thus provided for the vehicleoccupant without sacrificing the room available to him between steeringwheel 14 and his seat in the vehicle passenger compartment duringregular conditions. Further, this coextensive arrangement for upperjacket 44 will rigidify the support jacket assembly even though anintentionally weakened portion 52 is provided in one of the membersthereof, the intermediate jacket 42 serving to transfer to the upperjacket the rigidity present in the connection made by balls 46 and 48.This can be assured by firm engagement between these two jackets at theuncorrugated areas of the upper jacket, including the shear pinstrucutre therebetween.

Having thus described the invention, what is claimed 1. An energyabsorber comprising a first tubular member, a second tubular membersurrounding said first member and forming with the latter atelescopeable assembly, energy absorbing means connected between saidfirst and second members and operative upon the application ofpredetermined force in a direction causing telescoping movement of suchmembers to provide a first mode of energy absorption, a third tubularmember surrounding said second member and at least coextensivetherewith, means connecting one end portion of said third member withsaid second member against relative movement therebetween in said onedirection, said third member including an energy absorbing portionsubject upon the application of a predetermined force in said onedirection to controlled plastic deformation for axial shortening of saidthird member in said one direction toward said one end portion thereofto provide a second mode of energy absorption, and releasable meansconnecting said third member with said second member against relativemovement therebetween and releasable under-a predetermined forceselected to effect the order of occurrence of said first mode energyabsorption and said second mode energy absorption.

2. An energy absorber comprising a first tubular member, a secondtubular member surrounding said first member and forming with the lattera tleescopeable assembly, a plurality of deformer balls engaged betweensaid first and second members with predetermined interference fit sothat upon the application of predetermined force in a direction causingtelescoping movement of such members said balls roll over the walls ofsuch members and plastically deform such walls for a first mode ofenergy absorption, a third tubular member surrounding said second memberand coextensive therewith, means connecting one end portion of saidthird member with said second member against relative movementtherebetween in said one direction, said third member upon theapplication of a predetermined force in said one direction being subjectto controlled plastic deformation for axial shortening of said thirdmember in said one direction toward said one end protion thereof for asecond mode of energy absorption, and releasable means connecting theother end portion of said third member with said second member againstrelative movement therebetween and releasable under a predeterminedforce selected to effect the order of occurrence of said first modeenergy absorption and said second mode energy absorption.

3. in an energy absorbing collapsible steering column for automotivevehicles including a steering shaft interconnecting a steering wheeloperable by the vehicle operator and the vehicle steering gear, supportjacket means comprising a first lower support jacket member, a secondlower support jacket member surrounding said first member and formingwith the latter a telescopeable assembly, a plurality of deformer ballsengaged between said first and second members with predeterminedinterference fit so that upon the application of predetermined force ina direction causing telescoping movement of such members said balls rollover the walls of such members and plastically deform such walls for afirst mode of energy absorption, a third support jacket membersurrounding said second member and extending to said steering wheel tosupport the same and the adjacent end of said steering shaft on thevehicle, at least coextensively therewith, means connecting one marginalend of said third member with said second member against relativemovement therebetween in said one direction, said third member includingan energy absorbing portion extending from said marginal end of saidthird member and confined within a distance of the latter definedbetween the ends of said coextensive second member, said energyabsorbing portion upon the application of a predetermined force in saidone direction being subject to controlled plastic deformation for axialshortening of said third member in said one direction toward said onemarginal end thereof for a second mode of energy absorption, andreleasable means connecting the other end portion of said third memberwith said second member and releasable under a predetermined forceselected to effect the order of energy absorption between that of saidfirst mode energy absorption and said second mode energy absorption.

1. An energy absorber comprising a first Tubular member, a secondtubular member surrounding said first member and forming with the lattera telescopeable assembly, energy absorbing means connected between saidfirst and second members and operative upon the application ofpredetermined force in a direction causing telescoping movement of suchmembers to provide a first mode of energy absorption, a third tubularmember surrounding said second member and at least coextensivetherewith, means connecting one end portion of said third member withsaid second member against relative movement therebetween in said onedirection, said third member including an energy absorbing portionsubject upon the application of a predetermined force in said onedirection to controlled plastic deformation for axial shortening of saidthird member in said one direction toward said one end portion thereofto provide a second mode of energy absorption, and releasable meansconnecting said third member with said second member against relativemovement therebetween and releasable under a predetermined forceselected to effect the order of occurrence of said first mode energyabsorption and said second mode energy absorption.
 2. An energy absorbercomprising a first tubular member, a second tubular member surroundingsaid first member and forming with the latter a tleescopeable assembly,a plurality of deformer balls engaged between said first and secondmembers with predetermined interference fit so that upon the applicationof predetermined force in a direction causing telescoping movement ofsuch members said balls roll over the walls of such members andplastically deform such walls for a first mode of energy absorption, athird tubular member surrounding said second member and coextensivetherewith, means connecting one end portion of said third member withsaid second member against relative movement therebetween in said onedirection, said third member upon the application of a predeterminedforce in said one direction being subject to controlled plasticdeformation for axial shortening of said third member in said onedirection toward said one end protion thereof for a second mode ofenergy absorption, and releasable means connecting the other end portionof said third member with said second member against relative movementtherebetween and releasable under a predetermined force selected toeffect the order of occurrence of said first mode energy absorption andsaid second mode energy absorption.
 3. In an energy absorbingcollapsible steering column for automotive vehicles including a steeringshaft interconnecting a steering wheel operable by the vehicle operatorand the vehicle steering gear, support jacket means comprising a firstlower support jacket member, a second lower support jacket membersurrounding said first member and forming with the latter atelescopeable assembly, a plurality of deformer balls engaged betweensaid first and second members with predetermined interference fit sothat upon the application of predetermined force in a direction causingtelescoping movement of such members said balls roll over the walls ofsuch members and plastically deform such walls for a first mode ofenergy absorption, a third support jacket member surrounding said secondmember and extending to said steering wheel to support the same and theadjacent end of said steering shaft on the vehicle, at leastcoextensively therewith, means connecting one marginal end of said thirdmember with said second member against relative movement therebetween insaid one direction, said third member including an energy absorbingportion extending from said marginal end of said third member andconfined within a distance of the latter defined between the ends ofsaid coextensive second member, said energy absorbing portion upon theapplication of a predetermined force in said one direction being subjectto controlled plastic deformation for axial shortening of said thirdmember in said one direction toward said one marginal end thereof for asecond modE of energy absorption, and releasable means connecting theother end portion of said third member with said second member andreleasable under a predetermined force selected to effect the order ofenergy absorption between that of said first mode energy absorption andsaid second mode energy absorption.